1. Field of the Invention
This disclosure relates to sensors for detecting loads and moments applied to the sensor, and more specifically to a compact and robust sensor for detecting loads applied to the sensor in a single direction and moments applied to the sensor in a single plane.
2. Description of the Related Art
Modern, computer-controlled prosthetic devices have many advantages over conventional prosthetic devices. For example, computer-controlled prosthetic devices can allow the amputees to walk with limited fear of stumbling or falling, allow amputees to lead a more active lifestyle, and improve the likelihood that amputees can realize their full economic potential. It is desirable to extend these benefits to as many as is possible of the thousands of new amputees each year, and the millions of existing amputees.
A load and moment sensor that is both compact and robust would extend the benefits of the modern, computer-controlled prosthetic device to a broader cross section of the amputee population. Since the prosthetic device must be the same length as the intact limb of the amputee, a more compact sensor allows the prosthetic device to be used by amputees that are shorter in height, especially children. Furthermore, a more robust sensor allows the prosthetic device to be used both in harsher environments and in more aggressive activities such as construction, hiking, and various sports.
In addition, designing a single, compact sensor to measure both an applied load and an applied moment presents a difficult challenge. The need to have a usable load output and the need to have a compact sensor may be opposing requirements. For example, when a force is applied to the sensor at a point off center, it typically generates not only an applied load on the sensor, but also an applied moment on the sensor. The applied load and moment create strains in the sensor. As the force is shifted further off center, the strain induced by the applied moment increases while the strain induced by the applied load remains constant. At a certain point, the strain induced by the applied load will be so small relative to the strain induced by the applied moment that it will become very difficult to measure both strains in the same sensor. One solution to maintain balance between load-induced strain and moment-induced strain is to increase the physical size of the sensor in the plane of the applied moment thereby sacrificing compactness.
Thus, there is a need for a compact and robust load and moment sensor for detecting loads applied to the sensor in a single direction and moments applied to the sensor in a single plane.